[2nd_Amendment_Defender]

I have also heard that gasoline is more unstable than hydrogen. Is it true that gasoline tanks are more likely to explode than a hydrogen tank?

[MainFrame65]

Gasoline is highly flammable, but not explosive. Gasoline VAPOR is explosive IN AIR, within a particular range of mixture, but it has to be pretty warm to reach a sufficient vapor pressure. I don't know the numbers, but lets guess it is something like 15 to 30 percent. Hydrogen is ONLY a gas at conceivable temperatures and pressures, so it will always mix with air. But Hydrogen mixed with air is explosive over a much wider range of mixture - perhaps 10 to 70 percent. (No, I don't have real numbers)

As far as a tank exploding, a filled, sealed gas tank will not - no Oxygen. Same for a tank of Hydrogen, at ambient pressure. But as the gas tank empties, the air above it forms a mixture that is almost certainly explosive, although not very large. As a PRESSURIZED tank of Hydrogen empties, its content remains pure Hydrogen, so it would not become explosive - as long as you ignore the problem of extremely high pressure gas of ANY kind.

[MainFrame65]

I found some real numbers about explosive gas mixtures in air. the chart can be found at:

http://www.afcintl.com/pdf/combustibles.pdf

And the relevant numbers are:

LEL **** UEL **** Material

1.4% *** 7.6% *** Gasoline, 100 octane (vapor)

1.6% *** 8.4% *** Butane (gas)

3.3% ** 19.0% *** Ethanol (vapor)

6.0% ** 36.0% *** Methanol (vapor)

4.0% ** 75.0% *** Hydrogen (gas)

These are percentages by volume, at 1 atmosphere. LEL and UEL are LOWER and UPPER explosive limit, respectively.